Some of the plants we grow are of such ancient cultivation that no wild form is known; even though hybridization depends on an understanding of plant sexuality that doesn’t come about until well after the Middle Ages, people have been selecting and manipulating plant forms since the Neolithic.

At least one species common in Roman antiquity is thought to be extinct. (See http://en.wikipedia.org/wiki/Silphium.) The species known to the Middle Ages are still extant, although some of them may no longer be easily obtained in the horticultural trade because they have been supplanted by garden forms. In such cases, we acquire seeds from botanical gardens who maintain seed banks in the interest of biodiversity.

Although we know of named varieties of medieval fruits, named varieties of flowering plants don’t predate the Renaissance, when there was a significant increase in plants brought under cultivation, as well as a major shift in the way that plants were described and categorized. Many garden forms of the Renaissance have been lost to cultivation, although the species and more recent garden forms are still with us.